The durability of reinforced concrete is influenced by those physical characteristics of concrete that control the diffusion of gases, such as CO2 and O2 or of liquids (mainly water) through its pores, and the diffusion of ions, such as Cl-, dissolved in the pore water. These physical characteristics depend on the composition of concrete, the chemical composition and type of cement, and the relative humidity and temperature of the environment. In the present paper, these characteristics of concrete are determined analytically and/or experimentally in terms of the composition parameters and environmental condtions; the molar concentration of those constituents that are susceptible to carbonation; the porosity and pre-size distribution; the degree of saturation of the pores; and effective diffusivity of gases through the concrete.

Physical and Chemical Characteristics Affecting the Durability of Concrete

We thoroughly investigate and quantify the chemical stability of an imidazolium-based alkaline anion exchange polymerized ionic liquid (PIL), poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium hydroxide) (poly(MEBIm-OH), over a broad range of humidities, temperatures, and alkaline concentrations using the combined techniques of electrochemical impedance spectroscopy and nuclear magnetic resonance spectroscopy. High chemical stability was observed under dry conditions (10% RH) at 30 °C, humid and saturated conditions up to 80 °C, and even in mild alkaline conditions ([KOH] 1 M). Under these conditions, we suggest an imidazolium ring-opening mechanism as the primary degradation pathway, based on a detailed analysis of the 1H NMR spectra. Similar to poly(MEBIm-OH), other alkaline anion (carbonate (CO32–) and bicarbonate (HCO3–)) exchange PILs were als...

Relative Chemical Stability of Imidazolium-Based Alkaline Anion Exchange Polymerized Ionic Liquids

Flame inhibition of aluminum dust explosion by NaHCO3 and NH4H2PO4

Inhibition of aluminum dust explosion by NaHCO3 with different particle size distributions.

On the role of droplets in cocurrent annular and churn-annular pipe flow

A thermal gravimetric method was used to measure rates of decomposition of NAHCO3 particles. Such decomposition produces a highly porous Na2Co3 that reacts with SO2 rapidly and completely at moderate temperatures. Hence, NaHCO3 decomposition provides a reactant with attractive features for SO2 removal. The rapid rate of decomposition combined with the high heat effect prevented determining intrinsic rates by constant temperature runs when the temperature level was above 400 K. However, rising-temperature runs, which allowed time for heat transfer to equilibrate temperatures of the thermocouple and particles, gave reliable results at high temperatures. The activation energy was 102 kJ/mol. Porosimeter data verified the large increase in pore volume (from 0.03 to 0.39 × 10−3 m3/kg) on converting the NaHCO3 particles to Na2CO3. First-order kinetics were observed up to high conversions, after which the apparent order decreased. However, the sodium bicarbonate could be completely converted to Na2CO3.

Kinetics of sodium bicarbonate decomposition

A single-pellet, moment technique is presented for evaluating reaction rate constants, effective diffusivities, and adsorption equilibrium constants for gas-solid noncatalytic reactions. Experimental pulse-response data for the reaction of SO/sub 2/ with activated soda at 473 K were obtained to illustrate the method. The results show that intraparticle diffusion is the controlling mechanism for this reaction. The value of the Thiele modulus for axial transport was found to be 8.6 for a cylindrical pellet of porosity 0.56, tortuosity 2.3, and length 3 x 10/sup -2/ m.

Single‐Pellet, moment method for analysis of gas‐solid reactions

Macropore and micropore effective diffusion coefficients from dynamic single‐pellet experiments

Variations in pore structure cause significant changes in diffusion resistance and adsorption characteristics during the reaction of SO2 with activated soda. Breakthrough and moment analysis of the SO2-activated soda ash reaction showed that the effective diffusion coefficient of SO2 in the solid product (mostly Na2SO3) was about three times smaller than its value in the original activated soda. About 30% of the diffusion flux of SO2 in the solid product was found to be due to surface diffusion. The adsorption equilibrium constant of SO2 on the solid product was found to be about half the value of the adsorption equilibrium constant on activated soda. It was also determined that SO2 was irreversibly adsorbed on the solid product Na2SO3 at 200°C and 3.7 atm. The gaseous product CO2 was not adsorbed on the solid product while it was slightly adsorbed on activated soda.



Les ecarts intervenant dans la structure des pores entraǐnent des changements significatifs dans les caracteristiques d'adsorption et de resistance a la diffusion au cours de la reaction du SO2 avec de la soude activee. L'analyse de moment et de variation de l'effluent en fonction du temps de la rection du carbonate de soude active par le SO2, montre que le coefficient de diffusion effective du SO2 dans le produit solide (essentiellement du NA2SO3) est environ Vois fois plus petit que la valeur obtenue dans la soude activee d'origine. On a trouve qu'environ 30% du flux de diffusion de SO2 dans le produit solide dependait de la diffusion de surface. La constante d'euilibre d'adsorption du SO2 sur le produit solide represente la moitie de la valeur de la constante d'equilibre d'adsorption sur de la soude activee. Il apparaǐt egalement que le SO2 est adsorbe de maniere irreversible sur le Na2SO3 a 200°C et 3.7 atm. Le CO2 gazeux n'est pas adsorbe sur le produit solide alors qu'il est legerement adsorbe sur la soude activee.

Gülsen Doǧu

Papers

Kinetics of sodium bicarbonate decomposition

Single‐Pellet, moment method for analysis of gas‐solid reactions

Macropore and micropore effective diffusion coefficients from dynamic single‐pellet experiments

Dynamic analysis of changes in diffusion and sorption parameters in the reaction of SO2 with activated soda ash

Kinetics of catalytic oxidation of ethylene: fixed-bed and fluidized-bed studies